Contactless communication is a technology for wireless communication with an extremely-short range of up to 10 centimeters. Contactless communication is used in, for example, communication between IC cards and automatic ticket gates, communication between IC cards or mobile phones and automatic vending machines or electric cash registers, communication between IC cards and security systems, and electric power transmission to mobile devices such as cellular phones. Technologies of applying contactless communication are more recently being developed for use in chip-to-chip communication in three-dimensional integrated circuits, in addition to keyless entry for cars, data exchange between mobile devices and personal computers, and the likes.
Three-dimensional integrated circuits mean semiconductor integrated circuits that each contain two or more chips stacked and enclosed in a single package. In order to achieve more reduced sizes, expanded functionality, enhanced speeds, and reduced power, semiconductor integrated circuits need more increased degrees of integration. Finer design rules are approaching their limits too closely to further increase the degrees of integration in two dimensions. The three-dimensional integrated circuits have been thus developed to increase the degrees of integration in three dimensions.
Among chip-to-chip communication schemes for three-dimensional integrated circuits, development of those using through silicon vias (TSVs) precedes that of the others. TSVs are conductive material, such as copper, filled in through-holes that are opened in a silicon substrate by etching. TSVs are electrically connected with wiring layers in the same chip so that, when the chip is stacked on a different chip, the TSVs are further electrically connected with wiring layers of the different chip. This enables circuits embedded in each chip to exchange signals through the TSVs with circuits embedded in another chip. Since a number of TSVs can be provided in a single chip, the chip-to-chip communication can achieve a sufficiently large bandwidth. On the other hand, TSVs have too fine structures to easily achieve a more simplified process of manufacture or a more enhanced degree of reliability.
Application of contactless communication technologies to chip-to-chip communication in three-dimensional integrated circuits is expected to enable a structure simpler than TSVs to enhance its reliability. A chip-to-chip contactless communication scheme uses coil antennas. (Refer to, e.g., Patent Literature 1.) Coil antennas are antennas with a loop element shaped by a trace or line on a substrate; they are formed on each of two chips stacked on top of another. With these chips stacked, the loop element of a coil antenna on the upper chip is placed coaxially with that of a coil antenna on the lower chip. Accordingly, induction coupling between the coil antennas causes a change in electric current amount flowing through one of them to produce an electromotive force through the other. Using this phenomenon, circuits embedded on each of the chips can exchange signals with those embedded on another.